The treatment of waste water and sewage by electroflotation to remove impurities is well known in the art. Such treatment of waste water generally involves an initial electrocoagulation step in which the waster water is fed into an electrolytic cell where electrical impulses are applied to the water to generate a flock containing the impurities. A flotation step follows in which the flock rises to the surface of the water where it can be removed by mechanical methods external to the electrolytic cell. See for example, U.S. Pat. No. 3,726,780. The treated water and flock are re-used or disposed of appropriately.
WO 2011/023851 and WO 2011/018556 disclose electroflotation methods and apparatuses for purification of water involving separation of the flock from the treated water in an area located above the electrolytic cell. However, a problem with the apparatuses disclosed by WO 2011/023851 and WO 2011/018556 is that the flock aggregate is readily broken up by the turbulent water flow exiting the electrolytic cell thereby hampering separation of the flock from the treated water. This limits operation of the apparatuses to lower water throughputs to ensure adequate water/flock separation.
WO 96/15989 discloses a flock separating apparatus for use in sewage or sludge treatment. The apparatus has an electrolytic cell and a separating tank. The flock generated is carried upward out of the cell and into the separating tank by hydrogen gas produced in the electrocoagulation step. The flock continues to rise in the separating tank while the treated water passes from the separating tank into a receiving and discharge tank. Although such passage decelerates the climbing speed of the water relative to that of the flock thereby improving the water/flock separation efficiency, it is necessary for the receiving and discharge tank to have a surface area that is many times larger than that of the separating tank. WO 03/062152 discloses a method and apparatus for removing impurities from waste water by electroflotation. The waste water passes through an electrolytic cell with a wearing and a non-wearing electrode to produce a flock that is conveyed to a flock and purified water separation tower. Purified water and flock are conducted from the bottom and top ends of the tower respectively. The apparatuses of WO 96/15989 and WO 03/062152 require relatively complex engineering designs and a longer time is required to achieve separation of the flock from the treated water. This increases operation costs.
CA 1232570 A1 purportedly teaches an apparatus for electrochemical purification of contaminated liquids. A section of the coagulation chamber accommodated in the settling chamber and the separating wall are fashioned as truncated cones facing by their large bases the froth collector, the mixing chamber having perforated damping partitions. It would be desirable to provide an electroflotation apparatus that is simple in design yet capable of removing impurities from waste water at higher water throughputs whilst retaining an aggregate of the generated flock.